1. Field of the Invention
The present invention relates to a method for controlling the communication with mobile stations within a network, preferably in a WLAN (Wireless Local Area Network) according to the IEEE802.11 standard, wherein the network comprises at least one access point via which the stations are associated with the network, and wherein the stations can enter a power save mode.
2. Description of the Related Art
The IEEE802.11 standard does not only represent a widely accepted access technology to wireless local area networks (WLANs), but moreover, it is taken into consideration as hot-spot access technology to the Internet within cellular 3GPP systems or as access technology to the IP-multimedia subsystem (IMS). In order to ensure wider area coverage granting access to an infrastructure based on the IEEE802.11 standard as well, there is a need for efficient mechanisms to reduce the power consumption of mobile devices on the one hand, and routing states have to be maintained efficiently in the network in order to support the reachability of the mobile devices on the other hand.
The IEEE802.11 standard specifies fundamental mechanisms to support the network interface card (NIC) of mobile stations if they have entered a power save mode (PSM). Furthermore, the IEEE802.11 standard allows indication of data traffic as well as forwarding IP data packets that come in to IEEE802.11 access points (AP) to mobile devices having entered the PSM. The relevant configurations necessary are made during the association process between a mobile device and an IEEE802.11 access point. In this case, the mobile device informs the access point about the parameter regarding its Listen Interval (LI) and in exchange the access point assigns an association identifier (AID) to the mobile device. The full control of a mobile station in PSM is hence collocated with the access point, i.e. the access point maintains the state of the mobile station, buffers IP data packets destined to the mobile station in power save mode, and notifies the mobile station by a so-called Traffic Indication Bitmap (TIM) that packets are available and can be polled from the access point, i.e. can be taken from there. Finally, the access point forwards the buffered data packets to the respective stations when the station requests the packets by means of an IEEE802.11-specific signaling message (a so-called power save poll, PSP) packet by packet.
According to the above captioned description, the known method of controlling the communication with a mobile station in power save mode turns out to be disadvantageous in two ways. Due to the fact that the full control of a mobile station in power save mode is taken over by the access point with which the mobile station is associated, the above mentioned configuration, i.e. especially the AID assigned to the station by the access point, is only valid as long as the mobile station is associated with the access point. In a larger network with several access points, the configuration has to be renewed whenever the station associates with a new access point. This re-configuration involves additional data traffic which has especially bad impacts on the power consumption of the mobile station.
A further basic disadvantage must be seen in the enormous complexity access points have to show in order to be able to take over the full control of mobile stations in PSM. The complexity may be appropriate for utilization in LANs in order to make specific functions that are specific for wireless technology transparent to the whole remaining network. Especially in larger (mobile) communication networks, a strict 1:1 association between a mobile station and an access point means a drastic restriction regarding flexibility, though.